When throwing your Solgaleo or Lunala out, you can scroll to your ultraspace portal external move and use it as normal. However if you recall your pokemon and throw it back out, the image will go from grayed out to full upon the new throw. It's not actually resetting the cooldown, but resetting the graphic. Once you click the button once more, it shows how long the cooldown is.

This may not be a huge bug, but many players mistake it for the portal just not spawning (claiming the feature is broken).

Thanks for the report. I've passed this along to internal. We'll get this ticket updated when we know more.

This should now be fixed with the external move skill rework. Closing!